Conventionally, there have been developed techniques to irradiate an inspection subject with light, to capture the light reflected from a surface of the inspection subject as image data, and to detect abnormalities of the inspection subject based on a luminance variation of the image data.
In addition, there have been developed techniques to periodically vary the intensity of the light irradiating the inspection subject during the image caption and to detect the abnormalities based on the luminance variation of the captured image data.